As an apparatus which collects a pattern of unevenness of a skin surface optically, there is one which uses a triangular prism. Unevenness of a skin surface includes a fingerprint and a palmprint, for example. Hereinafter, a fingerprint image collection device using a prism will be described.
FIG. 22 is a diagram showing a structure of a fingerprint image collection device using a prism. On one face of a prism 2 (it is supposed that it is an upper surface), light is thrown from a light source 3 via another face at an angle equal to or more than the critical angle in the air. When an image sensor 4 is placed in a direction in which the thrown light is totally reflected by the upper surface, the image sensor 4 receives the light totally reflected by the upper surface via the further different surface of the prism 2. When making a finger 1 touch the upper surface of the prism 2, a surface of the skin of the finger does not touch the prism 2 in a valley part of the fingerprint. Therefore, light thrown on a valley part of a fingerprint is totally reflected by the upper surface of the prism 2. On the other hand, in a ridge part of the fingerprint, a surface of the skin of the finger touches the prism 2. Therefore, light thrown on a ridge part of the fingerprint is diffused at the contact zone without being reflected. Accordingly, when making a finger touch on the upper surface of the prism 2, a fingerprint image, in which a valley part of a fingerprint, at which light is totally reflected, is bright, and a ridge part, at which light is diffused, is dark, can be obtained at the image sensor 4.
Also, in patent literature 1, there is described an example of a body feature input apparatus that uses a film into which a plurality of V-shaped grooves which are identical in shape are formed, that is, a prism sheet instead of the above-mentioned prism is disclosed. Body features in the patent literature 1 includes a fingerprint, a palmprint, hand geometry, a footprint and the like.
FIG. 23 is a diagram illustrating a structure of a body feature input device of that document.
This body feature input device is a device made by changing the prism 2 of the above-mentioned fingerprint image collection device shown in FIG. 22 with a prism sheet 5. V-shaped grooves are formed at angle equal to or more than the critical angle in the air relative to the flat face of a prism sheet 5 (it is supposed that it is an upper surface). Light from the light source 3 is thrown via a face on which the grooves are formed. When the image sensor 4 is placed in a direction in which the thrown light is totally reflected by the upper surface, the image sensor 4 receives the light totally reflected by the upper surface. When making a finger 1 touch the upper surface of the prism sheet 5, a surface of the skin of the finger does not touch the prism sheet 5 in a valley part of a fingerprint. Therefore, light thrown on a valley part of the fingerprint is totally reflected by the upper surface of the prism sheet 5. On the other hand, a surface of skin of a finger touches the prism sheet 5 in a ridge part of a fingerprint. Therefore, light thrown on a ridge part of the fingerprint is diffused at the contact zone without being reflected. Accordingly, when making a finger touch the upper surface of the prism sheet 5, a fingerprint image, in which a valley part of a fingerprint, at which light is totally reflected, is bright, and a ridge part, at which light is diffused, is dark, can be obtained at the image sensor 4.
Meanwhile, in patent literature 1, there is a suggestion that a fingerprint image collection device is configured such that it obtains a fingerprint image by diffused light of a contact surface between a film and a finger, not by reflected light. In case a fingerprint image is obtained by diffused light, by photographing a part where a finger touches a film by the sensor 4, a pattern caused by a difference between intensity of the diffused light of a contact surface between the film and the finger and intensity of diffused light of skin of the finger in an area where the skin does not touch the film, which penetrates through the film, is obtained as a fingerprint image. (A convex portion of skin of a finger which touches a film and a portion corresponding to such convex portion in a fingerprint image are called a ridge line. Also, a concave portion of skin of a finger which does not touch a film and a portion corresponding to such concave portion in a fingerprint image are called a valley line.) In this case, a position of the sensor 4 is not limited to a position at which illumination light totally reflected by the upper surface of a prism sheet can be observed.